Donald Broadbent

Donald Eric Broadbent (Birmingham, 1926-April 10 1993) was an influential English experimental psychologist. His career and his research work bridged the gap between the pre-Second World War approach of Sir Frederick Bartlett and its wartime development into applied psychology, and what from the late 1960s became known as cognitive psychology.

Life

Broadbent was originally interested in the natural sciences, so upon joining the Royal Air Force (RAF) in 1944, he began to study aeronautical engineering. During his time in the RAF, he observed communication difficulties often arose from psychological, and not physical, causes. In particular, he noticed that inefficient processes of attention, perception, and memory were the causes of difficulties, rather than any failures of technical equipment or hearing. Having made this observation, Broadbent's interests began to zero in on psychology, leaving engineering behind.</ref name=wikibooks/> However, psychology was still virtually unheard of in England at that time. When Broadbent traveled to America, however, for flight training, he discovered that psychology was being widely studied.

Broadbent spent a short time working in the personnel selection branch of the RAF before beginning to his studies at Cambridge's psychology department. Due to its natural sciences orientation and its emphasis on practical application, Broadbent (and scores of other future psychologists) found Cambridge to be the ideal place for him. The department was headed by Sir Frederick Bartlett and was eager to apply newfound cybernetic ideals towards understanding human behavior, especially in terms of control systems, practical problems, and psychological theory in general. Broadbent found his place in the Applied Psychology Unit there.

In 1958, Broadbent became director of the Applied Psychology Research Unit which had been set up there by the UK Medical Research Council on Bartlett's persuasion in 1944. Although much of the work of the APRU was directed at practical issues of military or industrial significance, Broadbent rapidly became well known for his theoretical work. His theories of selective attention and short-term memory were developed as digital computers were beginning to become available to the academic community, and were among the first to use computer analogies to make a serious contribution to the analysis of human cognition. They were combined to form what became known as the "single channel hypothesis." His Filter Model proposed that the physical characteristics (such as, pitch, loudness) of an auditorily presented message were used to focus attention to only a single message. Broadbent remained director at the Applied Psychology Research Unit for 25 years, until 1974.

During this time, he also looked at problems caused by communication with gunnery and air control systems, in which many channels of communication were delivered at one time. This research contributed favorably to his research on attention and noise (something which, up until then, were considered unrelated). His research suggested that, although most people spend their lives surrounded by many different types of stimuli, they cannot respond to or describe the majority of them.

Broadbent's Filter model is referred to as an early selection model because irrelevant messages are filtered out before the stimulus information is processed for meaning. These and other theories were brought together in his 1958 book, Perception and Communication, which remains one of the classic texts of cognitive psychology..

In 1974, Broadbent became a fellow of Wolfson College, Oxford and returned to applied problems, developing new ideas about implicit learning from consideration of human performance in complex industrial processes along with his colleague Dianne Berry.

Broadbents Filter Model

Accounts for a theoretical filter device, which is located in between the incoming sensory register, and the short-term memory storage. His theory is based upon the multi-storage paradigm of William James(1890) and later [Atkinson-Shiffrin_memory_model](1968). This filter functions together with a buffer, and enables the subject to handle two kinds of stimuli, presented at the same time. One of the inputs is allowed through the filter, while the other is waiting in in the buffer for later processing. The filter prevents overloading of the limited capacity mechanism beyond the filter, which is the short-term memory. It is based on the famous cocktail party problem of the British scientist Colin Cherry, who is trying to explain how we are able to focus our attention towards the stimuli which we find most interesting.Broadbent comes up with the theory based on data from an experiment where three pairs of different digits are presented simultaneously, three digits in one ear and three in the other. Most participants recalled the digits ear by ear, rather than pair by pair. Thus, if 496 were presented to one ear and 852 to the other, the recall would be 496852 rather than 489562.

A lecture in Broadbent's honour is given at the annual conference of the British Psychological Society.

Legacy

1. Broadbent's filter is all-or-nothing (it does not allow through unattended messages), whereas Treisman's filter allows unattended messages through, but in an attenuated form. Treisman proposed this amendment to account for a number of empirical findings which were not explained by Broadbent. For instance, Moray (1959) had found that "subjectively 'important' messages such as a person's own name can penetrate the block [the all-or-nothing filter]: thus a person will hear instructions if they are presented with his own name as part of the rejected message". A similar finding by Oswald et al (1960) found that a person's own name and critical names presented to a sleeping subject elicited a clench response which had been previously conditioned. Treisman (1960), using a dichotic listening with shadowing procedure, found that if different sentences in the two ears are suddenly switched, then the subject shadows one or two words of the unattended message before reverting back to shadow the attended ear. Clearly, certain unattended messages can be processed semantically, hence the need to modify the physical characteristics filter.

2. Broadbent's is a simple single filter model, whereas Treisman's can be thought of as a two-stage filtering process: firstly, filtering on the basis of incoming channel characteristics, and secondly, filtering by the threshold settings of the dictionary units. Treisman's explanation as to the way these threshold settings perform a filtering operation explains the findings of Moray, Oswald and Treisman described above, and many other similar findings. The dictionary units have the two mportant properties of having thresholds that differ, and which are variable. Some units, those which respond to biologically (or emotionally) important signals, have permanently lowered thresholds. Hence, even very attenuated signals (because they are not being attended to) can trigger a unit which is 'tuned' to that signal. This explains the reason why one's own name can attract one's attention in a previously unattended message. On a more biological level, this explains the sensitivity that mothers have for the noises their babies make, even when virtually out of earshot. In addition to these semi-permanent threshold differentials, there is the transient variation in thresholds due to the expectations of the subject i.e. the context. The occurrence of a particular signal will, if it triggers a dictionary unit, lower the threshold for other signals which in the past have been associated with it. Hence, highly probably words (e.g. those half way through a sentence in Treisman's 1960 experiment) are made more likely to fire even if their signal is attenuated.

Notes

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